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JOURNAL, R.A.S. (CEYLON). [VOL. XVI. 



changes in the temperature, and in the degree of salinity of 

 the water, have the effect of rendering certain of the banks 

 untenable to the oysters for more or less prolonged periods. 

 Further, it is stated upon good authority that the strong 

 ocean currents from the Bay of Bengal, which sweep round 

 the coasts of Ceylon and Southern India, contribute largely 

 to the causes which denude the oyster banks. Altogether, it 

 will be seen that this question is one of some difficulty, and 

 that it must involve the solution of quite a number of local 

 marine problems. 



On the western coast of South America, which is likewise 

 at present being upraised from the sea,* pearl fisheries 

 formerly existed, which gave rise to wealthy and populous 

 cities — "whose very ruins have now perished." Yet, doubt- 

 less, some day Science will provide means for the revival of 

 these industries, possibly- — as in the case of the fisheries of 

 California — by the introduction of special diving apparatus ; 

 for, after all, it may be found that the oysters have merely 

 migrated seawards into deeper and more sheltered waters. 



In regard to the questions of artificial cultivation and 

 conservation, it is important to observe that the pearl oyster 

 —like the Strassburg goose — only becomes of special com- 

 mercial value when it has developed certain conditions of 

 organic disease. We have already seen that pearls must be 

 regarded as a pathological product, and we find this conclu- 

 sion well supported in the records of the fisheries. These 

 contain frequent references to the number of pearls found 

 in diseased and dying oysters ; and experienced divers are 

 apparently agreed that the probability of finding pearls is 

 always greater when the oysters are crowded together, and 

 become humped and distorted in shape,! and at the same 

 time afford cover for all kinds of marine worms and 

 parasitic creatures. Thus, unhealthy conditions of living 

 must presumably be encouraged in order to promote the 



* Darwin, " Naturalist's Voyage in the 4 Beagle.' " 



t These small thick oysters are called by the people " Koddai-pakku," 

 viz., "arecanut oysters" (Twynam's Report, p. 59). 



